Two methods of weaponizing ricin were explored: bullets and
shrapnel coated with ricin toxins or a 'dust cloud' of toxin
toxins inhaled into the lungs. The thermal sensitivity of ricin
to heat posed a problem as the firing of bullets and shrapnel
would disable the toxin. Military authorities decided to delay
development of the dust cloud until an antitoxin was
created.

Ouch, they didn't create an antitoxin first? Might want some
water around if you're playing with fire, no?

In any case, sixteen major nations signed the Geneva Protocol in
1925, promising never to use gas weapons in war ever
again (comically, the U.S. version sat in the Senate until
ratification in 1975).

Chemical weapons were eventually banned through and through with
the signing of the Chemical Weapons Convention in 1997.